Introducing: Thomas Valran and Samuel Viboud

We have presented all the scientists that are involved in the project, but still haven’t introduced the two most important people: Samuel and Thomas without whom we would not have been able to conduct the experiments.

Today, part 2: Samuel Viboud, for Thomas see here.

Samuel is an engineer in experimental techniques on large instruments and has been working at LEGI since 2001, when it was still at another place in Grenoble where Elin, Anna and Adrian conducted experiments about 10 years ago. To be in charge of the rebuild of the Coriolis platform was the most exciting event for him. Samuel is the technical director of the Coriolis platform and the head of the mechanical department at LEGI. Thanks to his creativity, technical know-how and sense for innovation, he received the well-deserved “Médailles de cristal” from CRNS in 2015.
About his personal life he says:
“Coming from a winemaker family who cultivates the grape varietal: “Mondeuse”, I live in the village of Apremont in Savoie, and do not hesitate to spend my time with work such as harvesting and bottling. In my personal life that I share with my wife and my 2 children, the exchange, the attention and the mutual support are daily. Concerning leisure, I am passionate about sport and particularly about road cycling. I regularly climb the mountain passes of the region and commute 100km to work by bike. The mountains are also my playground especially in winter, with ski touring that I like to share with my friends. What characterizes me in the end in life as at work are the essential values such as: sharing, conviviality and family.”

 

 

Introducing: Thomas Valran and Samuel Viboud

We have presented all the scientists that are involved in the project, but still haven’t introduced the two most important people: Samuel and Thomas without whom we would not have been able to conduct the experiments.

Today, part 1: Thomas Valran.
Part 2 to follow on Monday

Thomas is an engineer at the Coriolis platform and has been working for LEGI since March 2016. During his diploma in industrial engineering at the “Ecole nationale supérieure des Mines de Saint-Etienne” he worked as apprentice engineer for Schneider Electric. At the Coriolis platform, the most exciting part for him is to work for many different projects that never make the job boring. Due to his experience in climbing he moves on the supports of the platform very gently despite the high rotation speed. In his spare time, Thomas likes to go on road trips with his motorcycle or help at his parent’s farm where he grew up and where there are about 100 cows to take care of.

How salt changes the current

Until the beginning of the week we had only conducted barotropic experiments. This means that we induced fresh water into fresh water. How boring, you may thing… Well, although these experiments were very interesting, you are probably right because this setup doesn’t quite correspond to reality. At the coast of Antarctica, dense water is on one side produced by the growth of sea ice and on the other side origins from deep water that spills over the coast onto the continental shelf. Because the continental shelf slopes down towards the ice shelf, the dense water reaches towards the ice shelf. Our aim is to find out how the water behaves as it reaches the ice shelf front.

To reproduce this dense water flow, we inject salt enriched water into the channel. This relatively dense water approaches the ice shelf front along the left channel slope. To see a clear boundary between the dense and the fresh water, only a density difference of 1 kg/m3 is needed. The density difference increases the velocity of the current a lot, so that the experiments last much shorter. While the barotropic current was mainly blocked by the ice shelf front, the baroclinic current can freely enter the cavity beneath the ice shelf, as the dense water is largely decoupled from the freshwater. Because the fresh water layer above the dense current is barotropic, the previous experiments were of big interest as well to see how the upper layer behaves as the current reaches the ice shelf front.

On the cross section through the channel, the dense water separates clearly from the freshwater. It flows parallel to the slope to its left. Because we built a wall at the end of the channel (see our previous post: https://skolelab.uib.no/blogg/darelius/2017/10/20/closing-off-our-channel-at-the-ice-shelf-end-to-avoid-unrealistic-outflow/), the channel fills up quickly with salt water, which we have to evacuate after each experiment.

The dense, saline water contains many particles and gets visible in the vertical laser sheet. It flows towards the ice shelf (=towards us) along the slope to its left side.

In the photo of the cross section, you can also see 4 probes sticking in the water that we use to measure the density close to the source and close to the ice shelf front. We can then calculate the velocity of the dense current and the mixing between the fresh water and dense water along the channel.

In this experiment, we injected a flow that is 1kg/m3 denser than the ambient water. During the scans, the vertical laser shows the position of the dense current and the 4 probes (2 in front of the ice shelf front, 2 in front of the vertical laser) measure the change in density with time.

First impression of the ice shelf experiments

This week we have started new experiments that use a V-shaped channel sloping down towards an ice shelf front. More than a whole week was used to remove the topography for the shelf break experiments and to build up a new topography, readjust the cameras and set up the lasers.

After some days of experiments, you will finally get to see some first time lapse videos of the current flowing towards the ice shelf! In these experiments, we want to find out how the current behaves as it reaches the ice shelf front. How much of the water gets blocked as it reaches the ice front that corresponds to a large step in water thickness? Does the water manage to flow underneath the ice shelf? In which direction does it go when it gets blocked? And what is happening inside the ice shelf cavity? As in the previous experiments, we are using a barotropic current (no density difference between the inflowing and the ambient water) and compare it to a baroclinic current (denser inflowing water than the ambient water).

With our GoPro that is installed high the topography in the center of the tank, we can record the current inside the channel. In this case, a barotropic current flows towards an ice shelf that is lowered 30 cm beneath the surface and sits on the wings of the V-shaped channel.

One of the cameras is installed on the left side of the above gif about 10m behind the ice shelf. It looks into the channel facing the source. With this camera, we are able to observe if the current is barotropic or not.

With the vertical laser sheet, we can see the cross section through the channel. The cloud of particles shows the location of the current, coming towards the camera. The transition between the current and the ambient water is very vertical, which shows that the flow is barotropic.

You may think that it sounds very easy to produce a barotropic flow – we just need to use the same water for the inflow as for the water inside the tank. But in reality it turns out that the current is very sensitive to small density differences and the inflowing water easily gets buoyant as it is stored under the roof of the rotating platform! However, a higher rotation speed seems to reduce the sensitivity to the density difference!

Visit of VIPs for the opening of the “Fête de la Science”

“Fête de la Science” is a national event that promotes French science to the general public and gives access to research institutes and laboratories, including hands-on experiments, activities for the whole family and screening of movies. LÉGI is an important contributor for the region Isère and welcomed many important French people at the opening of the event on Thursday.

Here you can see the big crowd squeezed onto the surrounding platforms gazing at the rotating Coriolis tank, while Samuel and the director of the laboratory explained what kind of experiments they conduct in the lab. Unfortunately the tank was not filled with water yet, but the topography for our experiments that will start next week was mounted in the tank.

The laboratory with the Coriolis platform was filled with people glazing at the rotating platform during the opening of the “Fête de la Science”.

Among the visitors there were also journalists that interviewed Céline afterwards. It was screened on the local TV channel France3 and is available online: http://france3-regions.francetvinfo.fr/auvergne-rhone-alpes/emissions/jt-1920-alpes.

A short translation of what the journalists says in the beginning and what Céline explains about the background of the experiment:

Journalist: It looks like a big merry-go-round. Its name is Coriolis. With 13-m diameter, it’s the largest platform of its kind in the world. People come from all around the world to use it. Here, Swedish scientists are preparing their experiments that they will perform with a lot of instrumentation and nearly 1m of water height. They are studying the melting of Antarctic glaciers.

Céline: « Once the glaciers have melted, and have produced a relatively fresh water, what does this freshwater do ? To which depth does it sink, where does it go to, how does it mix with the rest of the water column, and which consequences does that have on the whole global ocean circulation ? »

 

Fluorescent dye and baroclinic experiments

As promised last week, here are some photos of the shining flow that contains fluorescent dye. To remove the green light from the laser, we used the polarized safety glasses that only left the illuminated current. Isn’t it pretty?

Adding fluorescent dye to the inflow water makes the current nicely visible. In the beginning of the experiment, the baroclinic flow turns around the first corner. The waves evolve due to the shear between the moving current and the still-standing ambient water.

 

Once the current has evolved and deepened, the part closest to the wall is barotropic and passes the first curvature without turning.

Whether the flow resembles the first photo or the second photo mainly depends on the strength of the inflow and the density difference between the inflowing and the ambient water. But the flow also evolves with time! That means, in the beginning the freshwater flow turns directly around the first corner, whereas it rather continues straight along the slope after a certain time. Let’s explain that in more details on some sketches:

Does this make sense to you?

The rotating swimming experience

Yesterday was the last day of experiments with the shelf break setup, before we will continue ice front experiments next week. To celebrate a (hopefully) successful series of many experiments without any big troubles (we’ve heard stories about a leaking tank, shut off electricity etc), we just couldn’t resist to go swimming in the rotating pool! Here you see how we were having fun!

Apparently, we are the first people that went swimming in the tank! It was not only fun, but we also got our personal experience of the Coriolis force that deflected us to the left while swimming. In addition, the water was mixed up for the following last two experiments, in which we induced fluorescent dye to get shiny pretty pictures of the current. Those photos will be coming next week…

Adding salt to spice it up

Today, we finally started some experiments that got us a bit closer to reality. The water in the tank is now salty, just like the Southern Ocean and the inflow is fresh, which produces a slope front. Remember, the slope front separates the warm deep water from the fresh shelf water influenced by the ice shelfs. The slope front makes it difficult for the warm deep water to get onto the continental shelf. We already wrote more about the ‘Antarctic Slope Front’ in a previous post (https://skolelab.uib.no/blogg/darelius/2017/09/19/a-bit-more-about-real-antarctica/).

On a photo of the camera of a cross section through the current you can actually nicely see this slope front!

Photos of the cross section of the inflow show the slope front that separates the fresh water from the salt water

 

To actually measure the change in density with depth, we attached 5 probes just above the current that do profiles of the water column. They measure the conductivity and temperature, from which we calculate the density. So, it is exactly the same as CTDs (conductivity – temperature – depth) that we use on the ship in Antarctica—just in miniature.

The 5 conductivity-temperature sensors that measure profiles of the water column to give us density profiles with depth.

 

After a while, the fresh water spreads out at the surface and forms a surface layer. When the laser crosses the interface between this surface layer and the salty subsurface layer it gets deflected, which we want to avoid. Therefor we were allowed to go into the tank and mix the water 🙂

To mix the fresh and the dense water, we were finally allowed to enter the pool while filled with water!

 

 

Turning images into data

Yesterday, the rotating tank was empty again and we used the whole day for an intensive session of data analyzing. Why was the tank empty again? We realized that the source was too close to the first corner when we used high inflow rates, so that the flow was not completely established once we reached the first corner. Therefore, we decided to move the position of the source 2m back to have a more established flow once it reaches the first corner. Samuel and Thomas did a great job with building a new slope and moving the source. However, it took quite some time to dry the glue, so that we had an empty tank yesterday and used this opportunity to process the data.

For the data processing, the people from the Coriolis platform provided us with the software UVMAT, which can conduct all the steps from the image to a velocity field. In a simplified way, the three images below show these different steps from one experiment that we did last friday.

 

 

 

 

Introducing: Nadine Steiger

I am Nadine and will spend the whole 2 months in Grenoble to make sure that I don’t miss anything exciting in the lab. Just one month ago I started my PhD with Elin in Bergen and I am still a bit new to the topic. So, I will be learning together with you and help keeping you up-to-date on what is happening at the Coriolis platform. My background is in meteorology and oceanography with a main focus on polar regions. Because I have been studying the retreat of marine-terminating glaciers during my master thesis, it really interests me why the beautiful ice has to melt! How does the warm ocean water can make it all the way into the ice shelf cavities and how will this change in a changing environment? I hope we will get closer to the answer during the experiments here in Grenoble.